Generally described, the turbine section and the compressor section of a gas turbine engine are coupled via a rotor shaft. A number of circumferentially spaced rotor blades may be attached to the rotor shaft in both sections. The rotor blades in the turbine section are driven by hot combustion gases. The rotor shaft in turn drives the rotor blades in the compressor section so as to provide compressed air. Because the casing of the compressor may have a different thermal response time than the rotor wheel or rotor blades therein, the rotor blade tips may expand at a different rate than the casing so as to create the potential for the rotor blades to rub against the casing. Such rubbing may cause early rotor blade damages and possible failure. As a result, operational rotor blade/casing clearances must accommodate these differing expansion rates. These increased clearances may limit the efficiency of the overall gas turbine engine.
Current compressor inlet casing designs generally incorporate either a separate bearing housing in an inner barrel or the inner bellmouth or may have an integrally cast bearing housing that is machined into a solid inner bellmouth lower half. The bearing housing includes a number of bearing pads positioned about the rotor shaft for support during rotation thereof.
During operation, the integrally cast lower half bearing housing may expand due to the temperature of the bearing lubricating oil so as to rise vertically relative to the centerline of the inner bellmouth. This expansion is due in part to the asymmetric mass and the stiffness of the integrally cast lower half bearing housing. The thermal rise of the bearing housing is not desirable because it may push the rotor shaft off center. The integrally cast bearing housing, however, is cheaper as compared to a separate bearing housing. Greater clearances thus may be required so as to avoid casing rubbing.
There is a desire therefore for an improved compressor inlet casing design so as to reduce or eliminate the impact of thermal expansion on an integrally cast bearing housing. Preferably such an improved design would maintain the rotor shaft in position so as to allow tighter clearances about the casing and the rotor blades for an increase in overall system efficiency.